Emissions from fossil fuel combustion facilities, such as flue gases of coal-fired utilities and municipal solid waste incinerators, typically include multiple types of gases. For example, emissions from a smokestack can include gases such as CO2, NO2, SO2, etc.
Many countries regulate emissions of the different types of waste gases because of potential environmental hazards posed by such harmful emissions. Accordingly, many facilities that generate or potentially generate harmful gas emissions need to employ multiple gas analyzer systems to ensure that emitted gases are compliant with corresponding regulations.
In certain cases, there are no particular regulations of certain types of emissions. In such instances, a flue operator may monitor different levels of constituents in a flue output for purposes of controlling a process. Thus, many applications for measuring contaminants such as SO3 and or H2SO4 are more for process control than for compliance emissions monitoring. To detect a presence of the many types of gases, a facility may need to operate multiple independent conventional gas analyzer systems and/or measurement benches. For example, a facility may need to operate a first gas analyzer system to detect a first type of gas, a second analyzer system to detect a second type of gas, and so on. Such instruments may combine multiple complex analytical technologies including electrochemical cells, chemi-luminescence spectroscopy, flame ionization and GFC (Gas Filter Correlation), NDIR (Non-Dispersive Infrared), UV (Ultra-Violet) Spectroscopy, etc., into a single gas analyzer unit to detect one or more types of gases.
Each of the different types of gases emitted by a smokestack has unique absorption characteristics. For example, each gas type can absorb different optical frequencies. The unique absorption characteristics enable a corresponding gas analyzer system to identify whether a particular type of gas is present in a gas sample.
A facility may need to operate multiple independent conventional gas analyzer systems and/or measurement benches to detect a presence of multiple gases of interest. Each conventional gas analyzer system typically requires its own set of operating procedures, calibration procedures, etc., to collect and generate accurate data.
One way to identify a type of gas present in an unknown gas sample is the application of Beer's law. In general, Beer's law defines an empirical relationship that relates the absorption of light to properties of the material through which the light is traveling. In other words, as mentioned above, different materials absorb different frequencies of light energy. Based on detecting which frequencies of optical energy are absorbed by the gas sample, it is possible to determine what type of gas is present in the gas sample. The amount of absorption by a sample can indicate a concentration of a respective gas.
Emissions of sulfur trioxide and/or sulfuric acid from a smokestack into the air may be undesirable for several reasons. Sulfur trioxide and/or sulfuric acid exiting a stack or chimney can add to air pollution. Sulfuric acid is a common agent in acid rain.
Also, sulfur trioxide can be very corrosive to equipment used in combustion facilities thus causing possible damage. Sulfur trioxide exiting a stack can appear as a blue plume, that is, exhaust smoke having a blue color adding to opacity and visual air pollution.
Selective catalytic reduction processes used to reduce other pollutants have created higher sulfur trioxide levels in flue gases. Such higher levels of sulfur trioxide have adversely affected removal of certain pollutants. For example, mercury is commonly removed from flue gases using activated carbon as part of an adsorption process. With higher levels of sulfur trioxide present during the adsorption process, the percent of mercury removed from flue gases dramatically decreases. Because of the potential environmental pollution and other negative effects, it may be useful to measure, monitor, and/or control sulfur trioxide emissions.
Conventional systems for analyzing a presence of sulfur trioxide can suffer from a number of deficiencies. For example, there are several types of detection systems that can be used to measure sulfur trioxide. Such systems include Fourier transform infrared (FTIR) spectroscopy, tunable diode laser spectroscopy, acid dew-point, conversion/fluorescence, filter correlation, and cavity ring-down systems. The current state of the art for measuring SO3/H2SO4 in flue gas is a wet chemistry approach referred to as Control Condensate, where a sample is extracted, the cooled SO3 in the presence of water forms H2SO4, which is collected and then chemically analyzed in a lab